No ported vacuum

[rockcrawlin]

I have a 1979 Chevy California Quadrajet.  I am getting full manifold vacuum at the vacuum advance port even with the idle backed all the down and the motor barely running.   Is it normal for some of this carb to have full vacuum, maybe for smog reasons or should I tear it apart?

[novadude]

I had a 49-state 1979 Chevy carb once, and I noticed the exact same thing.  The vacuum location on the carb body is full manifold.  It is not ported.  If you trace the path, it comes out under the throttle blades.  This seems to be normal for some models. 

There is a source that is "ported", but it the EGR port, and it has a "bleed hole".  Not the right one to use for ported vacuum advance.  This is on the front of the base, passenger side.  If you plug the round "bleed hole", I *think* that port should function like a normal ported source, but I am not 100% sure.

[Frank400]

Guys, I know this is an old thread, but I was working on a 17059217 today and the only ported vacuum source I could find on it (baseplate, front passenger side) had a very weak signal. 

    Followed the path and noticed that it has the usual slot opening just over the throttle blade, plus what seems to be some sort of bleed hole (like novadude is mentioning) a bit higher.  I plugged that hole and voilà, now full manifold vacuum once the throttle is cracked open, just like a ported vacuum source should be.

[Cliff Ruggles]

You located and used a ported source with a bleed off port to reduce the signal, most likely originally for EGR.

They work fine once the bleed off port is blocked as you found out.....Cliff

[ptaleo]

I have recently rebuilt a 17080213 and it pulls really good. The problem I have is I have no vacuum at either small ports. I can feel no pull at either, no change in the engine speed when they are open and also tthe idle mixture screws have no effect on engine idle. What do you think? Leo

[Frank400]

you mean no vacuum at idle ?  Do you have vacuum when you slowly open the throttle ?

[ptaleo]

I don't have vacuum at either port idling or part throttle. I replaced the base plate when rebuilding the carb. I laid them side by side and compared the holes and slots and they looked the same. It may be possible that the gasket may be covering something.